I've noticed using some browsers on some wireless networks (e.g. Barclays Bank free wifi) you get these errors with AW and also this site. It looks like some networks attempt to intercept the certs and modify/replace them with their own. My experience is that Opera is more likely to spot the intercept than other browsers.
In case you're wondering, no I wasn't checking AW while in Barclays Wank....I was in the pub across the road
